Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.82	13.617%	$255.4337	$255.43	$255.45	$255.40
Purchase #2	$171.71	10.356%	$189.4923	$189.49	$189.50	$189.50
Purchase #3	$250.30	7.669%	$269.4955	$269.50	$269.50	$269.50
Purchase #4	$104.37	11.627%	$116.5051	$116.51	$116.50	$116.50
Purchase #5	$7.33	10.754%	$8.1183	$8.12	$8.10	$8.10
Purchase #6	$48.78	8.435%	$52.8946	$52.89	$52.90	$52.90
Purchase #7	$175.79	7.437%	$188.8635	$188.86	$188.85	$188.90
7 purchase totals =	$983.10		$1,080.8030	$1,080.80	$1,080.80	$1,080.80